i think an antimatter weapon is like a RPG that fires rockets that inverts the explosion so the result of Explosion would be negative,instead of exploding everything it would anti-explode the result of it would be catastrophic it would destroy all the matter of the universe(cause its anti-matterHmm - an antimatter weapon wouldn't destroy all of the matter in the universe, for example if you drop an 1 kg antimatter bomb on a planet, it would annihilate with 1 kg of matter and release 1.8 * 1017 J of energy (2000 times the energy of the Fat Man bomb that hit Hiroshima). That would do a huge amount of damage to the planet, but definitely would not destroy all the matter in the universe. Assuming all mass in the universe is matter and if you by destroy mean matter-antimatter-annihilation, you would need an equal amount of antimatter plus you would need it to reach all the matter in the universe. I don't see any realistic way you could possibly make such a weapon, even in science fiction it wouldn't make any sense to me for such a thing to exist.
a bomb's yield in tons is the equivalent in tnt. so 5 mt would be 5 million tons of tnt worth of explosions.TIL it isn't literally weight